JPS583571A - Current detecting circuit - Google Patents

Abstract

PURPOSE:To accurately detect the AC current of a inverter by obtaining a signal proportional to the DC current of an inverter with a detector which can detect the normal and reverse current and dividing the signal by a signal proportional to the output frequency. CONSTITUTION:A voltage inverter is formed of a power converter 1, a smoothing capacitor 2 and a power inverter 3, thereby driving an induction motor 5. A detector 10 which can detect the normal and reverse current is provided in a DC line of the inverter, the voltage signal is divided by the voltage signal of a frequency controller 9 which supplies a trigger signal to a power inverter 3 in response to the output frequency by a divider 11, the prescribed coefficient K is then multiplied, thereby calculating the AC current of the inverter. Accordingly, the AC current of the inverter can be detected in the state that the current flowing through a motor 5 is discriminated to be drive current or regenerative current, thereby eliminating a phase difference detector and the like and simplifying the circuit arrangement.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current detection circuit used for detecting alternating current of a voltage source inverter.

Figure 1 shows the configuration of a voltage source inverter that uses an induction motor as a load. In the figure, 1 is a forward conversion section, 2 is a smoothing capacitor, 3 is an inverse conversion section, and 4 is a frequency control section that sets the inverter output frequency. Supply to 1.

A 55-year-old induction motor is connected to the output of the inverse transformer 113 as a load. 6 is an alternating current detection a(
For example, transformer 1! 1 is a three-phase bridge rectifier circuit for rectifying the output current of the alternating current detector 5g. 8 is a resistor connected between the output terminals of the rectifier circuit 1, and the output current of the inverter is connected between both terminals.

That is, the primary 11E number of I441Ih machine 5. In the above configuration, a circuit is configured to detect the output voltage of the inverter using an alternating current detector 6, a rectifier circuit 7, and a resistor 8. The output current of the inverter (primary current of the induction motor II5) is detected as the voltage V between both ends.

However, the electric M detection circuit with the above mechanism detects alternating current!
! Since the current is 1fiL, it is impossible to determine from the detected value whether it is the drive current of the induction motor @g or the regenerative current. If we dare to discriminate between the drive current and the regenerative current, a phase difference detection circuit or the like will be required, making the circuit configuration complicated.

The present invention is superior! This was done in consideration of the current problem, and it uses a DC current detector that can detect whether the current is forward or reverse to obtain a voltage signal proportional to the 1i-several current flowing in the DC line of the voltage source inverter, and converts this into the inverter output frequency. Divided by the proportional voltage signal, j! By multiplying the current by a required coefficient, it is possible to provide a current detection circuit that can detect the alternating current of the inverter in a state where it is determined whether it is a drive current or a regenerative current, although it has a simple circuit network configuration. purpose.

The present invention will be explained in detail below based on the illustrated embodiments.

FIG. 12 shows an embodiment of the present invention.

1 is a forward conversion unit, 2 is a smoothing capacitor, 3 is an inverse conversion unit, 5
9 is an induction motor as a load, 9 is a frequency control section, and the structure of the voltage source inverter is the same as the conventional one except for the frequency control 89. The frequency control section 9 has a function of supplying the toggle signal to the inverse conversion s3 according to the inverter output frequency, which is the same as the conventional one, but in this embodiment, the voltage V according to the frequency signal 6ζ is It has a structure that makes it look like it has a collar.

10 is installed on the DC line of the inverter; ii5; DC current detector 1 capable of direct and reverse current configuration; l
A voltage signal proportional to the direct Wt iron current Ip0 of the W or the like is used as the numerator input, and a voltage v1 proportional to the output frequency from the frequency control section 9 is used as the denominator input. U is the side 14I! This is a coefficient multiplier that calculates the alternating current of the inverter by multiplying the output of 11J by a required coefficient k.

Therefore, in the Hx diagram, 0. DC voltage is 1° - DC current is O - AC output voltage of the inverter is 1°.

Set the frequency to 1. If the alternating current is ρao and the power factor of the induction motor 1 m5 is oos #, then Equation (1) holds true.

vDa""DO=4 VaO bow. -aos #
---(1) From formula (1), the alternating current work ac is -
obtained as. Now, the inverter is vac /y (-
K)" is controlled to be constant, then (
2) Formula - is expressed as. Furthermore, if we consider the direct tll voltage vD0 to be constant!・1 engineering. -K 7 □7 ・・・・・・・・・(4. Tabo, ni/ is a constant.

Here, if we intend to detect current in a range where the power factor oos- in equation (4) is approximately constant, then
° above, , , , , , (5). I asked,
K" is a constant.

That is, from direct current. By detecting this and dividing it by the frequency 1 at that time, the AC current 1 & 0 at that time will be detected 8. DC current flItxDo is Hall Igfi
It is detected by the ltR converter lA10, and the change in the direction of the current during the first regeneration when the inverter is driven is the direct current Ipc.
Voltage vIDa I: @ −ID. (a: [
It appears as a change of extreme regret in a). 't, the voltage proportional to the inverter output frequency 1 y = b @ y (11:
The coefficient) is obtained by the frequency control section 9, and the voltage V is calculated by the 1 divider V. Division is performed using n as the numerator and voltage Vν as the denominator. The voltage vD obtained by multiplying the output of the divider n by a coefficient k in a coefficient unit u is proportional to the primary current IaO of the induction motor 5, and the polarity of the driving current and the same-sex current are different.

That is, the detection output VD is expressed as shown in equation (6), and the alternating current Eyu. is detected and at the same time whether it is the drive current or not.
It is determined whether it is a same-sex current. In addition, the coefficients may be modified as appropriate.
! In addition, when the frequency control unit 9 is configured with an i microcomputer or the like, #C is the 1st division 1iiU, the coefficient aS is omitted, and the frequency is calculated by converting 0 from the DC current into a digital quantity using a converter. The primary current of the induction motor is calculated by digitally dividing using the frequency data of □, , read into the control unit 9 for frequency control. It is also possible to obtain a configuration in which the value is obtained as a digital quantity, and furthermore, a configuration in which this is converted into a Vm and displayed as an analog quantity.

As described above, according to the present invention, when detecting the alternating current of a voltage source inverter that supplies inductive load-ζ power such as an induction motor with a back electromotive force, a substantially constant power factor range, an inverter control mode, etc. Focusing on the fact that there is a certain relationship between the inverter's alternating current, direct current *S, and output frequency under certain conditions, we developed a direct fill system that can detect direct current and reverse current.
The numerator 1 of both signals is detected by a current detector, and a voltage signal proportional to the frequency is obtained from the inverter output from the frequency control section.
Since the alternating current is calculated by simple arithmetic processing such as division using the denominator, the inverter's alternating current can be accurately detected with a simple circuit configuration, and the drive current can be determined from the polarity of the detection output. IIWt can be easily determined.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional example of a current detection circuit for detecting the alternating current fM1 of a voltage source inverter, and FIG. 2 is a block diagram showing an embodiment of the current detection circuit according to the present invention. 1... Forward conversion unit, 2... Smoothing capacitor, 3...
Inverse conversion unit, 5... Induction motor, 9... Frequency control unit, 10... Hall current converter, 11... Divider,
12...Coefficient unit.

Claims (1)

[Claims] (1) A DC IIE current detector that is connected to the DC line of the voltage source inverter and generates a voltage signal proportional to the DC current, which can be configured to direct or reverse the current, and a voltage signal proportional to the inverter's output frequency. , the numerator input is a voltage signal ° proportional to the DC current, and the inverter output frequency −ζ
A current detection circuit comprising: a divider that receives a proportional voltage signal as a denominator input; and a coefficient multiplier that calculates an alternating current of an inverter by multiplying the output of the divider by a required coefficient.